There are many applications and markets today where much effort is being invested to develop sensor technologies that have greater performance in terms of sensitivity (parts per million or billion) and specificity (unambiguously detecting identified molecules) while offering the economics needed to deploy in a large scale to provide both qualitative and quantitative data to improve safety, their infrastructure and to better the environment. One example of such a need is around natural gas sensing (methane), a common energy source around the world. In the United States there are over 68 million homes and over 6 million buildings and thousands of factories that rely on natural gas. This gas is delivered via over 2.4 million miles of main gas pipelines having distributing pipes extending to homes/buildings and factories. This is a common means of distributing energy in major cities around the world. As with any infrastructure, the pipes continue to age and are prone to hazardous leaks. Natural gas is a highly combustible odorless and colorless hydrocarbon gas largely composed of methane. Gas leaks present a serious safety and environment hazard and much effort has been invested in developing higher sensitivity and specificity sensors. The need to deploy sensors extending to residential homes and buildings has placed price/performance criteria on sensors that are not currently satisfied by existing technologies. The primary performance concerns with existing commercial sensors are that they do not have specificity and hence generate false positives to common household agents; level of detection is not sufficient and the range of sensing is limited.
The Oil and Gas industry also utilize a wide variety of gases that present safety and environmental issues if not widely monitored for leaks. In the United State, Leak Detection And Repair (LDAR) programs are required as part of the Federal Regulations. A LDAR program is a facility's system of procedures used to locate and repair leaking components (e.g., valves, pumps, connectors, compressors, and agitators) to minimize fugitive Volatile Organic Compounds (VOC) and Hazardous Air Pollutants (HAP) emissions including but not limited to methane.
It is desirable to have methods apparatuses, and systems for tunable light source cavity detection using a plurality of axial-plus-transverse modes.